Hot Water Furnace Temperature Q&A

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Dear NH,

I have a problem with the temperature of the water in my home. I
have a hot water heating system, and my water is heated by the same
furnace. I do not have a hot water tank. Instead, the water comes
directly from the furnace. According to my oil burner company, I must
keep the temperature of the water in the furnace above 140 degrees or
my heating system will not work properly. This seems to be extremely
hot and I am concerned that my little one (when he is old enough to
reach the faucet) may burn himself. Should I insist he lower the
furnace temperature?

PB from Scranton, PA

PB,

You are without-a-doubt correct to be concerned about your water
temperature. Back in the good old days, it was not uncommon for water
heaters to be set at 160 degrees, more than hot enough to cause
instant severe burns! Nowadays, the standard setting for
hot water is between 110 and 120 degrees.

However, I would advise against changing the water temperature of
your furnace. Your furnace guy (or gal) is absolutely correct. Lowering the temperature will radically change the built-in efficiency
of your furnace and of your heating system as a whole.

Think about it… if you lower the temperature of the furnace, the
temperature of the water circulating through your radiators will
likewise be lowered. This will in turn increase the amount of time it
will take for your home to be heated. All things being equal, it takes
the same amount of oil to keep your home at a certain temperature
regardless of how hot the water is. Therefore, your oil burner will
have to cycle on and off more often to maintain this lower temperature
because it will take longer for the temperature to rise. This will
cause increased wear and tear on the furnace without any gain (or even
a loss) in efficiency. The most inefficient moment in your furnace's
operation is when it first starts up!

So instead of focusing on the furnace as the culprit, you can take
measures to lower the faucet hot water temperature AFTER it leaves the
furnace. This is done through the installation of a "mixing
valve". A mixing valve is a simple thermostatically-controlled
mechanism that mixes a little cold water with the hot water to lower
the temperature. Mixing valves are adjustable to product the desired
water temperature, but it is wise to use a thermometer to verify the
temperature at the tap. Installation does require some plumbing skills
such as pipe cutting and soldering, but the end result is worth it!